I am in the process of changing the brake pads on my 87 4-Runner. It has the S12+12 calipers (4WD IFS 4-piston). I got the driver's side completed so far. However, the top front piston on the passenger's side will not go back into the caliper. It moved in only a fraction of an inch and will not move any further. The other 3 went in fine. I tried removing brake fluid from the system and then tried taking the caliper off and using a C-clamp however that did not work either. I pulled the cylinder boot and set ring and tried to remove the piston but I can't figure out a good way to pull it out. Any information on this subject would be greatly appreciated. Anyone have any experience rebuilding these calipers? This happen to anyone else? I need this thing back on the road by tomorrow.

 

You've either got the piston cocked in the bore, or there's a bunch of corrosion in there jamming it. One way to get pistons out is blow air into the caliper, if you've got compressed air. If you do this watch your fingers, they usually come flying out hard.

If it's that corroded a rebuild probably won't be very successful. Once the finish is gone from the piston bores they will corrode much faster. You'll probably find the caliper jams, and will eat up your new pads quickly. I would just buy a rebuilt one.

 

Just got a rebuild one from AutoZone. $28.99 + tax saves me time trying to rebuild the old one and saves my front end because I can stop my truck now without rear ending someone. Has a lifetime warranty as well .

 

Sounds like a good deal, for that price it isn't worth even trying to rebuild it.